Laminate flooring usually consists of a core of a 7-8 mm fiberboard, a 0.2-0.8 mm thick upper decorative surface layer of laminate and a 0.1-0.6 mm thick lower balancing layer of laminate, plastic, paper or like material. The surface layer provides appearance and durability to the floorboards. The core provides stability and helps, together with the surface layer, to give the floorboard sufficient impact strength. The balancing layer keeps the board plane when the relative humidity (RH) varies during the year. The floorboards are laid floating, i.e. without gluing, on the subfloor. Traditional hard floorboards in floating flooring of this type are usually joined by means of glued tongue-and-groove joints (i.e. joints involving a tongue on one floorboard and a tongue groove on an adjoining floorboard) on long side and short side.
In addition to such traditional floors, which are joined by means of glued tongue-and-groove joints, floorboards have recently been developed which do not require the use of glue and instead are joined mechanically by means of so-called mechanical locking systems. These systems comprise locking means which lock the boards horizontally and vertically. The mechanical locking systems are usually formed by machining of the core of the board. Alternatively, parts of the locking system can be formed of a separate material, such as aluminum, which is integrated with the floorboard, i.e. joined with the floorboard in connection with the manufacture thereof.
The main advantages of floating floors with mechanical locking systems are that they can easily and quickly by laid by various combinations of inward angling and snapping-in. They can also easily be taken up again and used once more at a different location. A further advantage of the mechanical locking systems is that the edge portions of the floorboards can be made of materials which need not have good gluing properties.
Laminate flooring and also many other floorings with a surface layer of plastic, wood, veneer, cork and the like are made by the surface layer and the balancing layer being applied to a core material.
The first generation laminate flooring, so-called HPL flooring, was made by providing a 6 mm thick particle board with a 0.8 mm surface layer of decorative high pressure laminate, usually referred to as HPL. HPL is made in a separate operation where a plurality of impregnated sheets of paper are compressed under high pressure and at a high temperature to a laminate board.
Later the second generation laminate flooring was developed, which is based on a more modern principle where both manufacture of the decorative laminate layer and the fastening to the fiberboard take place in one and the same manufacturing step. Impregnated sheets of paper are applied directly to the board and pressed together under pressure and heat without any gluing. As a rule, the surface layer is about 0.2 mm thick. This direct laminated flooring, usually referred to as DL flooring, whose main advantage is that the production cost is lower, was first inferior to HPL flooring owing to, inter alia, a lower degree of impact strength and lower moisture resistance. The quality properties of the DL flooring, however, were significantly improved when the particle board was replaced by a qualified HDF type fiberboard—high density fiberboard. The HDF board was considerably harder than the particle board and more resistant to moisture. Thus, the impact strength and moisture resistance of the DL flooring could be improved. As this HDF board was also being manufactured in increasingly larger volumes, the cost was reduced and DL flooring with an HDF core became number one on the market. Although the particle board is considerably cheaper than HDF, the DL technology combined with HDF is altogether less expensive. DL flooring now had quality properties equivalent to those of HPL flooring but was at the same time essentially less expensive.
At this time when DL flooring was being sold in larger quantities than HPL flooring, the laminate flooring was joined using a traditional locking system consisting of tongue, groove and glue. HPL flooring with a core of particle board was easier to glue than DL flooring with a core of HDF. When the mechanical joint systems were developed, also this problem was eliminated, and in a short time DL flooring with a core of HDF captured 90% of the market.
In addition to the above two methods, a number of other methods are used to manufacture floating floors and provide different core materials with a surface layer. A decorative pattern can be printed on the surface of the core, which is then, for example, coated with a wear layer. The core can also be provided with a surface layer of wood, veneer, decorative paper or plastic sheeting, and these materials can then be coated with a wear layer.
As a rule, the above methods result in a floor element in the form of a large board which is then sawn into, for instance, some ten floor panels, which are then machined to floorboards.
In all cases, the above floor panels are individually machined along their edges to floorboards. The machining of the edges is carried out in advanced milling machines where the floor panel is exactly positioned between one or more chains and bands mounted, so that the floor panel can be moved at high speed and with great accuracy past a number of milling motors, which are provided with diamond cutting tools or metal cutting tools, which machine the edge of the floor panel. By using several milling motors operating at different angles, advanced joint geometries can be formed at speeds exceeding 100 m/min and with an accuracy of ±0.02 mm.
JP-20011329681 discloses a floorboard having a multilayer core and a surface layer comprising wood veneer and a vapor proof layer arranged between the veneer and the core. The core comprises a middle layer of plywood and upper and lower layers of MDF.
Definition of Some Terms
In the following text, the visible surface of the installed floorboard is called “front side”, while the opposite side of the floorboard, facing the subfloor, is called “rear side”. The sheet-shaped starting material that is used is called “core”. When the core is coated with a surface layer closest to the front side and preferably also a balancing layer closest to the rear side, it forms a semimanufacture which is called “floor panel” or “floor element” in the case where the semimanufacture, in a subsequent operation, is divided into a plurality of floor panels mentioned above. When the floor panels are machined along their edges so as to obtain their final shape with the joint system, they are called “floorboards”. By “surface layer” are meant all layers applied to the core closest to the front side and covering preferably the entire front side of the floorboard. By “decorative surface layer” is meant a layer which is mainly intended to give the floor its decorative appearance. “Wear layer” relates to a layer which is mainly adapted to improve the durability of the front side. In laminate flooring, this layer as a rule consists of a transparent sheet of paper with aluminum oxide added, which is impregnated with melamine resin. By “reinforcement layer” is meant a layer which is mainly intended to improve the capability of the surface layer of resisting impact and pressure and, in some cases, compensating for the irregularities of the core so that these will not be visible at the surface. In high pressure laminates, this reinforcement layer usually consists of brown kraft paper which is impregnated with phenol resin.
By laminate flooring is meant a floor board with a surface layer of a thermosetting laminate comprising one or more paper sheets impregnated with a thermosetting resin.
A core consisting of wood slates which are glued to a surface and balancing layer of wood is called “lamella core”. The slates have a fiber orientation which is perpendicular to the fiber orientation of the surface and balancing layers
The outer parts of the floorboard at the edge of the floorboard between the front side and the rear side are called “joint edge”. As a rule, the joint edge has several “joint surfaces” which can be vertical, horizontal, angled, rounded, beveled etc. These joint surfaces exist on different materials, for instance laminate, fiberboard, wood, plastic, metal (especially aluminum) or sealing material. By “joint edge portion” are meant the joint edge of the floorboard and part of the floorboard portions closest to the joint edge.
By “joint” or “joint system” are meant coacting connecting means which connect the floorboards vertically and/or horizontally. By “mechanical locking system” is meant that the joining can take place without glue horizontally parallel to the surface and vertically perpendicular to the surface. Mechanical locking systems can in many cases also be joined by means of glue which could be applied in the joint or between the rear side and the subfloor. By “floating floor” is meant a floor with floorboards which are only joined along their respective joint edges and thus not glued to the subfloor. In connection with movement due to moisture, the joint remains sealed. Movement due to moisture takes place in the outer areas of the floor along the walls concealed under the base boards. By “HDF” are meant board materials that are referred to on the market as high-density fiberboard. HDF consists of ground wood fibers joined by means of a binder. By particle board is meant a board material comprising wood particles joined by means of a binder.
The above techniques can be used to manufacture laminate floorings which are highly natural copies of wooden flooring, stones, tiles and the like and which are very easy to install using mechanical joint systems. The length and width of the floorboards are as a rule 1.2*0.2 m and the thickness is as a rule 7-8 mm.
Recently also laminate flooring with other formats and other thicknesses have been introduced on the market. Formats having a length of 1.2 m, a width of 0.4 m and a thickness of about 11 mm are used, for instance, to imitate stones and tiles. Laminate floor may also be produced in lengths of 1.8-2.4 m and widths of 0.2 m. All such floorboards will be heavy and difficult to handle in connection with transport and installation since HDF has a density of about 900 kg/m3. Besides the cost of material for an 11 mm HDF core is high. There is thus a great need to lower the cost and also the weight of the core in a thick or large laminate flooring board, but also in laminate flooring of normal thickness. The same applies to similar flooring having other surface layers such as veneer, plastic etc. For parquet flooring with a surface layer of 2-3 mm hardwood and a lamella core, the cost of the surface layers is considerable. The market for floating floors could increase significantly if the cost of the floorboard could be lowered and if the weight could be reduced.
Laminate flooring has a hard surface layer which produces a high sound level in the room as people walk on the floor, wearing shoes. This is a disadvantage that reduces the possibility of using the floor especially in public surroundings.
Prior-Art Technique And Problems Thereof
To facilitate the understanding and description of the present invention as well as the knowledge of the problems behind the invention now follows with reference to FIGS. 1-3 in the accompanying drawings.
FIGS. 2a-2c show manufacture of an HPL flooring. A wear layer 34 of a transparent material with great wearing strength is impregnated with melamine with aluminum oxide added. A decorative layer 35 of paper impregnated with melamine is placed under this layer 34. One or more reinforcing layers 36a, 36b of core paper impregnated with phenol are placed under the decorative layer 35 and the entire packet is placed in a press where it cures under pressure and heat to an about 0.5-0.8 mm thick surface layer 31 of high pressure laminate (HPL). FIG. 2c shows how this surface layer 31 can then be glued together with a balancing layer 32 to a core 30 to constitute a floor element 3. Due to the separate gluing operation, HPL flooring may be produced with a variety of different core materials such as HDF, particle boards and plastic material sheets. All HPL floors are however produced with a core of one material only.
FIGS. 2d and 2e illustrate manufacture of a DL flooring. A wear layer 34 in the form of an overlay and a decorative layer 35 of decoration paper is placed directly on a core 30. All three parts and, as a rule, also a rear balancing layer 32 are then placed in the press where they cure under heat and pressure to a floor element 3 with a decorative surface layer 31 having a thickness of about 0.2 mm. Direct laminate has usually no reinforcing layer. The capability of the laminate edge to resist impact and moisture is quite dependent on the properties of the core material. Therefore use is made of a high quality material with high density and moisture resistance such as HDF. The cost of material for HDF is significantly higher than that for particle board. The production method of direct lamination is a factor that limits the possibilities to use various core materials since the decorative layer is fixed to the core by the melamine resins in the decorative paper. The resin penetrates into the wood fibers of an HDF material and binds the surface layer to the core. The majority of all DL floors are produced with a HDF core. Some low quality floors are produced with a core of MDF or particle board. All DL floors however are based on a core made of a single material.
FIG. 3a shows an example of a traditional laminate or veneer flooring with a surface layer 31 of, for instance, direct laminate (DL) or 0.6 mm veneer, a core 30 of HDF and a balancing layer 32 of laminate or veneer that are joined by tongue, glue and joint. FIG. 3b shows an example of a laminate flooring with a surface 31 of HPL, a core of HDF and a mechanical locking system which consists of a strip 6 and a locking element 8 of aluminum and which coacts with a locking groove 14 formed in the core 30. In order to fix the strip to the core and to reach sufficient locking strength, the core is generally made of HDF.
FIG. 3c shows an example of a laminate flooring with a surface 31 of DL, a core 30 of HDF and a mechanical locking system 6, 8, 14 which has been formed from the core 30 of the floorboard. A core of HDF is in this case necessary for the locking system to obtain the required strength and function. The surface layer 31 could be wood or HPL. A wood surface could be combined with a core of HDF or plywood consisting of different wood layers which may be made of different wood materials.
FIG. 3d shows an example of a laminate flooring with a surface 31 of DL, a core of HDF and a mechanical joint system with a locking element 8 and a locking groove 14 in the upper part of the tongue groove.
FIG. 3e shows a parquet flooring, seen from the long side, with a thickness of about 15 mm, which has a surface layer 31 of e.g. 3 mm oak. The core consists in this example of different kinds of wood. A harder kind of wood 30a, 30b is to be found at the joint edge portions forming the mechanical locking system 7, 7′. Between these joint edge portions, the core 30 consists of wood slats 30c made of a soft and inexpensive kind of wood. The slats 30c are joined with the surface layer 31 and the balancing layer 32 by gluing. They often contain knots, cracks and the like. The surface layer 31 of wood must have a sufficient thickness to bridge these irregularities as well as the joints 37 between the slats 30c of the core. Such a lamella core is generally les expensive than an HDF core and gives a more stable floor board.
These floorboards suffer from a number of problems which are above all related to cost and function.
The HDF core that is required to give a laminate flooring or veneer flooring sufficient impact resistance in the surface and at the joint edges has substantially the same high quality in the entire floorboard. The density of a HDF core might vary between the parts closest to the surface and some other parts in the centre of the core but all parts contain the same type of wood fibers and binders. This overall high quality is not necessary, for instance, in the inner and rear parts of the floorboard.
Penetration of moisture into a floorboard takes place above all in the upper portions of the joint edge closest to the surface and it is in these portions that the HDF material is necessary. In the other portions of the floorboard, lower quality properties would be sufficient.
To be able to form a mechanical locking system with projecting parts, the joint edge and thus also the core of the floorboard must as a rule be of good quality. Also in this context, the high quality is only necessary in certain parts of the joint edges.
A parquet flooring with a lamella core has a wear layer of about 3 mm. This is needed above all to give the surface sufficient impact strength and to bridge the spaces between the wood slats of the core so as to prevent them from telegraphing through the surface layer and becoming visible in the surface. The surface layer is currently protected by a strong varnish and regrinding takes place only rarely or not at all. Consequently, the thickness of the wear layer could be reduced if the remaining problems could be solved.
The above problems result in a high cost of material and a high weight. The hard surface produces an undesirable sound level.
To counteract these problems, different methods have been employed. The main method is to reduce quality and density of the HDF board. DL flooring is also made with a particle board as core material. These methods result in a lower cost and a lower weight, but at the same time the impact strength is insufficient, the boards are sensitive to moisture and the mechanical joint systems have low strength and a poor function.
Parquet flooring is made with a core of particle board, HDF or plywood. As a rule, these materials are more expensive than a core of slats. A core of slats also reduces the board's movement due to moisture better than other board materials since the slats of the core are placed perpendicular to the longitudinal direction of the board. This means that the fiber direction of the slats is perpendicular to the fiber direction of the surface layer. Such a fiber orientation is favorable to counteract movement caused by moisture.
To reduce the sound level, floating laminate flooring is installed on a sound-absorbing layer of plastic foam, rag paper, textile fiber and the like. These layers have also been glued to the balancing layer of the rear side. This form of sound absorption yields a poor result and the cost is high.